Impregnation of Ni-P metal into polymer substrate via catalyzation in Sc-CO2 and electroless plating in Sc-CO2 emulsion

In this study we investigated the impregnation of Ni-P metal into polymer substrate via catalyzation in supercritical carbon dioxide (Sc-CO2) and electroless plating in Sc-CO2 emulsion, in comparison with calculated CO2 diffusion in polymer on the basis of Fick's law. Sc-CO2 has two major effects, high diffusivity and good chemical affinity with polymer, on the impregnation of Ni-P metal into the polyimide substrate. Our group fabricated an Ni-P thin film in Sc-CO2 With an electroless plating emulsion after catalyzing the Sc-CO2 with Pd complex. According to an EDX analysis, an increase in the Sc-CO2 catalyzation time led to increases in both the intensity and depth of the Ni-ion penetration into the polyimide. We found that the impregnation reaction of Ni by our novel method is CO2 diffusion controlling reaction. To clarify which of the two Sc-CO2 properties, diffusivity or chemical affinity, played a dominant role, we conducted an electroless plating reaction with emulsion using hexane as the catalyzation solvent whose diffusivity is lower than that of Sc-CO2. The good affinity with polyimide in the hexane catalyzation led to a film fabrication of Ni-P thin films, but numerous cracks were visible on the films under microscopic observation. According to an EDX analysis of the Ni-P catalyzed in hexane, the intensity of the penetrated Ni-ions into the polyimide was very low. The high diffusivity of the Sc-CO2 promoted the penetration of the Pd catalyst and Ni-P electroless plating solution into the polyimide substrate. (C) 2009 Elsevier B.V. All rights reserved.